DE102007062492B4 - Process for the production of a cementitious shaped block and manufactured molded block - Google Patents

Abstract

A method of producing a cementitious shaped block having a compressive strength of 3 to 20 N / mm 2 and a bulk density of 1 to 1.5 kg / dm 3, comprising the steps of preparing a mixture having an effective water to cement ratio of 0.35 to 0, 60, consisting of particles consisting of pre-aerated aerated concrete crushed granules with a particle size of up to 10 mm, 150 to 400 kg / m3 of hydraulically hardening cement, up to 20% by weight hard coal fly ash, max. 50 wt.% Of inert aggregates selected from sand, quartz sand and gravel and one volume of water, pressing the mixture at a pressure of 3 to 25 N / mm 2 into a mold, the mixture compressing a vibration of 30 to 200 Hz, and allowing the pressed mixture to cure.

Description

The present invention relates to a cementitious shaped block and a method for its production. The cementitious shaped stone according to the invention has a specific weight or bulk density of 1.0 to 1.5 kg / dm ³ , and can thus be referred to as Leichtstein; the compressive strength is 3 to 20 N / mm ^2, which is sufficient for use as a component for load-bearing walls in building construction. The molded block according to the invention is characterized in that it consists of recycled aerated concrete in a cement matrix.

State of the art

As aerated concrete a mineral building material is called low density, for example, with a bulk density of 0.3 to 1.0 kg / dm. ³ Aerated concrete is produced by autoclaving a foamed mixture of quicklime, quartz sand and water, optionally additionally with cement and / or gypsum. This foamed mixture is formed by adding a blowing agent, preferably aluminum powder, which triggers gas generation, which leads to pore formation in the mass. The foamed mixture has sufficient stability to be cut into desired shapes. The curing takes place in an autoclave in a saturated steam atmosphere at 180 to 200 ° C for up to 12 h.

Unlike normal concrete, in which quartz sand, gravel or other inert fillers are incorporated into the cementitious matrix resulting from the hydraulic hardening of the cement with water, the quartz sand or silica flour undergoes reaction in the autoclave treatment of the foamed mixture to form the reaction the matrix so that quartz sand or flour is not present as an inert filler in aerated concrete.

In the crushing of aerated concrete, for example, in the recycling of already built-in aerated concrete, or when drilling or milling of cellular concrete resulting flour can not be recycled so far. This is due to the porous structure of the cellular concrete, which can be described as cavities defining or cavities enclosing calcium silicate hydrate matrix. Due to this structure of the aerated concrete, the particles of the aerated concrete crushed granulate are also referred to herein as porous particles of calcium silicate hydrate matrix.

That's how it describes DE 199 31 898 C1 a process for the production of aerated concrete from quartz powder, hydraulic binders and water, in which the mass is exposed after foaming in a mold exclusively vertically directed vibrations to reduce the content of mixing water, the pores remain more evenly distributed over the cross section of the cellular concrete ,

The crushing of aerated concrete leads to a very large proportion, for example up to 50 wt .-% or more of aerated concrete crushed or aerated concrete crushed granules with a low strength of the particles, which is too low, for example, for use in road construction. Due to the instability of compressed aerated concrete crushed sand, or granulate used here, it is only permitted in small quantities as an ingredient in compacted substrates. In the recycling of concrete fracture fracture material made of aerated concrete is also only limited permitted, currently in a maximum weight of max. 5% by weight. The reason for strictly limiting the fraction of aerated concrete crushed or aerated concrete granules as aggregate in cementitious materials is that the addition of aerated concrete fracture material in any event compromises the strength and structure of the final product in conventional processing.

The DE 102 42 524 A1 describes lightweight concretes which have a content of expanded polystyrene and therefore have a reduced thermal conductivity with reduced compressive strength. For the recycling of lightweight concrete with polystyrene, the melting of the expanded polystyrene is proposed to remove it from concrete fracture. In preparing the invention, it has been found that a reason for excluding the addition of aerated concrete crushed granules to cementitious molding compositions is that when mixing a composition having a different content of aerated concrete crushed granules, the consistency of the aerated mixture becomes poorer, namely stiffer and less deformable, and moreover the homogeneity of the mixture is impaired, for example by the agglomeration of porous concrete granules. This impairment of the homogeneity of a mixture for producing cementitious stones containing aerated concrete crushed granules resulted in defects in the blank, which in turn reduced the strength of the finished brick. Due to the low strength of the aerated concrete crushed granules, sufficient compaction, for example by vibration, can not be achieved, which also causes the formation of voids in the molding.

The DE 19735063 A1 describes the coating of concrete aggregates of dense and porous structure, whereby a moisture barrier effect is achieved.

The DE 10354711 A1 describes porous granules produced from building material waste with an aerated concrete content of 20 to 70 percent by mass and their use. The granules are coated with a mixture of clay and clay and then fired at high temperatures.

The DE 1811033 A describes an aggregate for lightweight concrete from porous grains and a method for producing this aggregate. The aggregate consists of steam-hardened, spherical aerated concrete particles and / or porous concrete particles with a sealed or compacted surface.

The DE 4324974 A1 describes a process for producing a lightweight aggregate waste aggregate for a high quality insulation material, whereby the aerated concrete fracture is fired to close the pores.

The DE 2524147 A1 describes a method for producing wallboard from vapor-cured gas concrete fracture and / or gas concrete waste material.

The DE 19931898 C1 describes a process for the production of cellular concrete from quartz powder, hydraulic binder and water.

Object of the invention

In view of a lack of utilization possibility for porous concrete fracture granules, for example, with a particle size of <1 mm to <8 mm, the present invention has the object to provide a molded block with sufficient strength and sufficiently low thermal conductivity, at least in part, preferably exclusively from sufficiently solidified aerated concrete crushed granules exists, which can then be used as a building material.

General description of the invention

The invention solves this problem by providing a cementitious shaped block according to claim 11 and a method for its production according to claim 1. The molded block according to the invention has in a cement matrix incorporated particles of aerated concrete, wherein the cementitious matrix is hydraulically cured cement into which the particles of cellular concrete are involved.

Optionally, the cementitious shaped block according to the invention may contain additives, preferably hard coal fly ash, or inert additives, for example selected from the group comprising sand, in particular quartz sand, sand with a grain size of up to 4 or 5 mm and gravel. Preferably, the cementitious shaped block according to the invention consists solely of particles of aerated concrete, which are incorporated into a hydraulically cured cement matrix. The particles of aerated concrete, which can be referred to as the cavities limiting calcium silicate hydrate matrix or as particles of porous calcium silicate hydrate matrix according to the usual method of production of aerated concrete, are preferably derived from aerated concrete or aerated concrete granulate, for example, recycled aerated concrete, from the rubble processing or aerated concrete particles that are produced during drilling or milling of cellular concrete.

The shaped brick according to the invention is characterized by a compressive strength in the range of at least 3 N / mm ^2, preferably 5 to 20 N / mm ^2, preferably 10 to 15 N / mm ² and an apparent density of about 1 to 1.5 kg / dm ³ out.

The properties of the molded block according to the invention can be achieved by the production process according to the invention for this, in which aerated concrete granules are mixed with cement and water, optionally with the addition of hard coal fly ash and / or inert additives and optionally with the addition of liquefying additives and pressed into a mold. According to the invention, the mixture is compressed during the pressing, namely by vibration during the application of the pressing pressure. Preferably, the vibration is one-dimensional or two-dimensional in a plane perpendicular to the effect of the pressing pressure.

The starting mixture of aerated concrete granules, cement, which is preferably Portland cement, and optionally additives has a content of water, the suction capacity or the core moisture content of the aerated concrete granules used to its water saturation plus the volume of water of hydration for the cement, plus the water of hydration for corresponds to reactive additives. In the preferred embodiment, the shaped brick has no inert additives such as sand or gravel, but consists only of aerated concrete granules in a cement matrix, so that the starting mixture of aerated concrete granules, water, cement, without inert additives such as sand or gravel, and having a water content, the is composed of the suction capacity of the aerated concrete granulate to its water saturation and the water of hydration plus processing water for the cement. In this way, the cementitious shaped brick according to the invention is produced from a mixture having a water content which gives the mixture a so-called earth moisture, i. that the mixture is pourable, but is not flowable.

It is preferably provided to use aerated concrete granules in the water-saturated state, ie the proportion of the added water volume of the starting mixture, which corresponds to the suction capacity of the aerated concrete granules, is already contained in the aerated concrete granules. In this embodiment of the process of the invention, water-saturated aerated concrete granules are mixed with cement and a volume of water equal to the volume of water of hydration plus the processing water of the cement. In this process, the result is a particularly homogeneous distribution of aerated concrete granules in the cement matrix of the block, a small number of defects and thus a higher strength, as in a process, in which non-water saturated, eg dry porous concrete granules, water and cement are mixed to form the starting mixture.

Surprisingly, the present invention shows that cementitious shaped blocks can be made from aerated concrete granulate in which the weight fraction of aerated concrete granulate significantly exceeds the weight fraction of other inert aggregates, for example of sand or gravel, and the aerated concrete granules are incorporated into a cement matrix, wherein the molded block has sufficient strength having.

These advantageous properties of the molded block according to the invention are achieved by the process for its preparation, namely by pressing a humid starting mixture with simultaneous vibration of the starting mixture when the pressing pressure. The compressive strength and low thermal conductivity of the molded block are surprising in view of the known low stability of aerated concrete granules in the compression, and its low pressure stability in the mechanical mixing of the components for a homogeneous distribution of the starting mixture. For neither the pressure used in the production, nor the mixing of the starting mixture prevent sufficient compressive strength of the green body or the hardened molded block. In particular, the compressive strength of the cementitious shaped block was surprising in view of the during the production of the molding from the starting mixture by pressing with simultaneous vibration due to the known low strength or lack of compaction ability of porous concrete fracture granules.

The production of a cementitious shaped block from a mixture consisting essentially of cement, water and compressible aerated concrete crushed granules, which has a breaking point of about 4 N / mm ² , by pressing with a pressure exceeding the breaking point, eg from 4 to 25 N. / mm ² , preferably at 6 to 20 N / mm ² , is surprising because the resulting molded block immediately after the pressing process has a sufficient green strength and after curing has a strength that is well above the strength of the aerated concrete fracture granules used and also over the strength the intact aerated concrete lies.

The vibration according to the invention during the pressing of the starting material to the green compact can be carried out under low mechanical loading of a press plant, since a vibration at frequencies of 30 to 200 Hz, preferably 40 to 50 Hz during the pressing is sufficient. For the pressing pressure values of 5 to 20 N / mm ^{2 are} preferred, in particular of about 6 N / mm ² , which give similar compressive strengths of the cured shaped blocks, such as pressing pressures of 10 N / mm ² or higher.

The inventive method also has the advantage that it manages without thermal treatment of the green compacts, since solely by the hydraulic hardening of the cement, a cement matrix is formed, in which the particles are incorporated aerated concrete, so that the method including the curing are carried out at room temperature can.

As an alternative to curing at room or ambient temperature, the greenware can be accelerated at temperatures up to 70 ° C for 1 to 10 hours under ambient pressure to accelerate the curing.

The cement content of the starting mixture is in the range of 150 to 400 kg / m ³ , preferably between 200 and 370 kg / m ³ , particularly preferably between 270 and 370 kg / m ³ . The ratio of water to cement (W / Z value) can be in the range of 0.40 to 0.50, for example 0.48, in order to adjust the earth-moist consistency of the starting mixture according to the invention.

In addition to cement, non-hydraulic binders may be included in the starting mixture, preferably between 80 and 350 kg / m ^{3 of} burned or quenched lime.

Hardening of the green compacts may be carried out at ambient conditions, preferably under hydrothermal conditions, e.g. in a saturated steam atmosphere at 180 ° C up to 200 ° C for up to 12 h.

Detailed description of the invention

The invention will now be described in more detail by way of example with reference to the figures, in which:

1 shows the green strength of the starting material according to the invention immediately after pressing,

2 the compressive strength of the stones of 1 after a curing time of 28 days at room temperature as a function of the vibration during the pressing of 50, 100, 150 or 200 Hz in a direction perpendicular to the effect of the pressing pressure and the pressing pressure (N / mm ² ),

3 shows a comparison of the green strength, fresh mortar density, dry bulk density after curing for 28 days, and compressive strength after 7 and 28 days with and without vibration during pressing,

4 shows the influence of a flow agent on the density of the green compact, here referred to as fresh mortar, as a function of the vibration frequency during the pressing,

5 the green strength of the pressed starting materials of 4 shows,

6 the Trockenrohdichten after 28 days curing of the moldings of 4 shows,

7 the compressive strength of the moldings of 4 after curing over 28 days shows

8th shows a comparison of the green strength, the degree of compaction and the compressive strength of the blanks after 7 or 28 days curing time for starting mixtures in which the aerated concrete granules dry or water saturated (pre-wetted), with different cement contents,

9 shows an overview of the influence of the presence of a flow agent in the starting mixture on the green strength, dry bulk density, compactness, the degree of compaction, and the compressive strength of the molded articles after curing for 28 days for the preparation of the starting mixture with dry cellular concrete granules (PBtr) or mixtures of the starting mixture with water-saturated aerated concrete granules (PBvorg),

10 shows an overview of the compressive strength of shaped stones according to the invention as a function of the cement content of the starting mixture,

11 an overview of the influence of the cement content for cement CEM I 32.5 R and CEM I 42.5 R on the green strength, the degree of compaction, the dry bulk density and the compressive strength after curing of the pressed moldings over 7 or 28 days .

12 the influence of an addition of hard coal fly ash on the green strength, the green density, the dry bulk density and the compressive strength after curing for 7 or 28 days,

13 shows the compressive strength of shaped stones according to the invention following the pressing by postcuring at room temperature,

14 the side view of a pressing block according to the invention,

15 the damage of a molded block according to the invention which has occurred following the test for compressive strength,

16A shows the dry bulk density over the cross-section of moldings of starting mixture according to the invention along the effect of the compacting pressure at different vibration frequencies,

16B the distribution of the dry bulk density over the cross section of a molded article of inventive starting material along the effect of the pressing pressure without superplasticizer shows and

16C shows the distribution of dry bulk density with flux in the starting mixture,

17 the dry bulk density across the cross-section of a molded article of starting composition according to the invention along the effect of the pressing pressure for dry or water-saturated porous concrete granulate from which the starting mixture was prepared,

18 shows the effect of lowering the W / Z value on the dry bulk density distribution over the cross-section of a blank along the effect of the pressing pressure and

19 a micrograph of the structure of a molded block according to the invention shows.

Example: Production of cement-bonded shaped blocks made of water, cement and aerated concrete granules

Cement-bonded shaped blocks were produced from aerated concrete crushed granules, which were separated from rubble as granulation 0/2 mm from autoclaved aerated concrete 0/8 mm. This aerated concrete crushed granules contained about 17 wt .-% abmdable components and had a mean grain density of 1.24 g / cm ³ at a core moisture content of about 40 wt .-%. As cement Portland cement CEM I 32.5 R, available from the company. Teutonia, was used to 370 kg / m ³ starting mixture. The volume Mixing water was determined as the sum of the water volume used to saturate the suction capacity of the aerated concrete granulate, ie to reach its core moisture content, and the volume of water required for the hydration of the cement. The W / Z ratio was set to values between 0.42 and 0.50 unless otherwise stated for individual examinations.

Inert aggregates, for example sand or gravel, were used as starting mixtures in proportions of 10 to 50% by weight, without significantly impairing the strength values.

The starting mixture, which can also be referred to as fresh mortar, had the desired earth-moist consistency, which left the fresh mortar free-flowing and allowed no flow. The consistency of the starting mixture remained essentially unchanged for at least one hour after the addition of cement and mixing. Already in the preparation of the starting mixture showed that water-saturated aerated concrete granules led to a much stiffer consistency of the starting mixture, as dry used aerated concrete granules, although mathematically the mixture had the same total water content, namely the water volume required for water saturation of the aerated concrete granulate plus that for the hydration of the cement required volume of water.

The starting mixture was pressed about 60 minutes after mixing with a pressing pressure of 15 N / mm ² . When measuring prismatic specimens (PK) with the dimensions 40 mm × 40 mm × 160 mm, the flexural tensile strength was determined to be 3.0 to 3.8 N / mm ² , the compressive strength to 14 to 19 N / mm ² and dry densities of From 1.32 to 1.36 g / cm ³ .

In the preparation of the starting mixture with water-saturated aerated concrete crushed granules higher strength of the stones were achieved in the rule. It is currently believed that the use of pre-wet or water-saturated aerated concrete granules to make the starting mixture results in the W / Z ratio being lower since the water content attributable to the saturation of the suction capacity of the aerated concrete granules has already been absorbed by the latter; before the cement is mixed. Therefore, the cement paste forms at a W / Z ratio approaching the optimum target size, namely an available water content corresponding to the volume of water required to hydrate the cement. The higher flexural and compressive strengths measured for preformed aerated concrete granules are associated with higher dry bulk densities over molded bricks prepared from parent blends using dry aerated concrete granules, or those having a water content below core moisture ,

To form molded bricks, a mold having a clear internal volume of 10 cm × 10 cm × 10 cm was used with a single-sided pressure die, whereby the mold could be vibrated perpendicular to the action of the pressure punch.

The starting mixture for the subsequent experiments was prepared from 370 kg / m ³ Portland cement CEM I 32.5 R, dry aerated concrete crushed granules 0/2 mm at a W / Z ratio of 0.48. The green strength was measured immediately after compaction under a compacting pressure in 1 and 2 is measured under vibrations at 50, 100, 150 and 200 Hz. The compression strength of molded bricks was determined after 7 and 28 days curing at 20 ° C and 98% relative humidity.

1 shows that green strength increases with higher frequency of vibration and higher pressing pressure. A maximum green stand strength was achieved here at pressing pressures of about 6 N / mm ² .

2 shows that substantially the same compressive strength of about 10 N / mm ^{2 is} achieved at a pressing pressure of 6 N / mm ² to about 8 N / mm ² after curing for 28 days, substantially independent of the vibration frequency during pressing.

From the in 3 As shown in the results, it was found that the starting mixture with a compacting pressure of 6 N / mm ² and a vibration at 200 Hz produced a sufficiently high green strength and compressive strength of the hardened molded block.

A preferred embodiment of the invention is to add to the starting mixture a liquefying additive, for example a conventional concrete liquefier or a flow agent, for example a detergent, e.g. Melaminharzsulfonat. The results showed that by adding flow agent better processability of the starting mixture substantially the same compressive strength after hardening of the green compact over 28 days was achieved.

In detail shows 4 in that the fresh mortar density was higher due to the addition of the flow agent (FM) at the vibration frequencies used. 5 shows that the addition of the flow agent lowers the green strength, especially at lower vibration frequencies during pressing; 6 shows that the dry bulk density depends on the vibration frequency is reduced during the pressing by the addition of superplasticizer, wherein this decrease at 200 Hz vibration is lower. 7 shows that the compressive strength of the block after hardening of the green compact for 28 days at vibration frequencies during the pressing of 50 Hz and 200 Hz are hardly affected, while after compression at vibrations of 100 and 150 Hz higher compressive strengths are achieved for starting mixtures to which flow agent was added ,

It is preferred that the aerated concrete book granules used in the starting mixture is water saturated. This can be achieved by mixing the aerated concrete crushed granules with a volume of water for 5 to 15 minutes required to achieve water saturation, and then admixing the cement and mixing water with a volume corresponding to the required water of hydration of the cement.

In a conventional mortar stirrer, the components of the mixture can be mixed homogeneously and the mixture can be pressed to the green compact within a period of at least 1 h. For vibratory pressing, conventional vibrating presses may be used, such as e.g. be used in concrete block production.

In 8th an overview of the green strength and the degree of compaction and the compressive strength of the blocks after curing for 7 or 28 days is shown using dry or water-saturated aerated concrete granules (PB), and different cement contents of the starting mixture. These results show that with lower cement content of the starting mixture, pre-soaked aerated concrete crushed granules lead to a reduction of the green strength and with a low cement content of the starting mixture somewhat reduced compressive strength after hardening. At higher cement content, although the green strength is reduced, the compressive strengths after curing were substantially unchanged or are slightly increased. The degree of compaction also increases with higher cement content in starting mixtures in which water-saturated aerated concrete crushed granules were used.

9 shows the influence of the flow agent at a cement content of the starting mixture of 370 kg / m ² , a pressure of 4 N / mm ² and a vibration of 200 Hz. The addition of superplasticizer leads to an increase in the compaction, but also to a reduction in the green stability and the compressive strength after 28 days of curing. When adding a superplasticizer to the starting mixture using water-saturated aerated concrete crushed granules in the starting mixture, the computational degree of compaction increases to 100% and the compressive strength after 28 days of curing reaches a maximum of> 13 N / mm ² .

The reduction of the added volume of mixing water by 10 wt .-% leads to an increase in green strength, but to a degree of compaction of only 98%, while the compressive strength drops to 8 to 9 N / mm ² , as without the addition of superplasticizer and / or was achieved with non-water-saturated aerated concrete granules in the starting mixture.

Overall, it is therefore preferable, in particular in the exemplary starting mixture, to produce the starting mixture of water-saturated aerated concrete crushed granules with an addition of superplasticizer, without reducing the volume of mixing water.

10 shows that at cement contents of 270 to 370 kg / m ³ starting mixture sufficient compressive strengths of the cured conglomerates were achieved.

A comparison of the values of different starting mixtures with Portland cement CEM I 32.5 R versus those with CEM I 42.5 R is in 11 shown using cement contents in the starting mixture of 270 or 300 kg / m ³ . The measurement results show that the compressive strength increases with higher cement content, regardless of the quality of the cement and regardless of the water content of the aerated concrete crushed granules used. As the cement content increases, the degree of compaction of the compacts also increases, with the exception of the starting mixtures with CEM I 42.5 R with a higher cement content, the green strength increases as well. Furthermore, it can be seen here that with the cements used, the compressive strength achieved after 28 days hardening reaches a similar value. Therefore, shaped bricks according to the invention can also be produced with Portland cement with the quality CEM I 32.5 R without adversely affecting the final strength of the molded bricks.

The addition of hard coal fly ash (SFA), an artificial pozzolan, to 10 wt .-%, based on the amount of cement in the starting mixture did not lead to a consistency change, but to an increase in the green strength of the compacts. In the 12 However, the measured values reported show that the degree of compaction and the compressive strength of the blocks did not increase from the hard coal fly ash content after 7 and 28 days of hardening.

However, for a starting mixture with 350 kg / m ³ cement, use of water-saturated aerated concrete crushed granules and flux as described above, pressing the starting mixture at 6 N / mm ² at a 200 Hz vibration, an increase in hardness over 90 days of cure could be noted. In relation to the compressive strength after 28 days, the compressive strength increased to about 12.2 N / mm ² , which represents an increase of 23% compared to the hardness after 28 days, which is essentially due to the content of hard coal fly ash. It is therefore preferred according to the invention to also add 5 to 20% by weight hard coal fly ash in combination with pre-mixed aerated concrete crushed granules and flow agents in the starting mixture.

14 shows the side view of a compact, wherein the punch in the image acted from above. The side view shows a density gradient along the pressing direction.

15 shows a molded block after performing a compressive strength test in which the load in the image was vertical. The shape of the fracture zone in the shaped brick shows that the higher-density layers which are at the top in terms of the pressing pressure show less cracking, while a distinct cracking occurs in the lower, lower-compacted area.

The investigation of the dry bulk density of compacts was examined over the cross-section in slices (S 1 ascending to S 7 from bottom to top), the press die acting from above. Surprisingly, it was found that samples with a pronounced density gradient tend to have a higher compressive strength.

Non-fluidized samples have steeper density gradients, with density increasing with vibrations from 50 Hz to 100 Hz to 150 Hz; At 200 Hz vibration, the lowest layers show the lowest densities and the upper layers the highest densities if no flux was added ( 16A ). A uniform density distribution was found for vibrations of 50 Hz in the compression, while higher vibration frequencies cause greater density gradients. Furthermore, the dry bulk density (TRD) decreases with increasing frequency.

The influence of the addition of flow agent to the starting mixture on the dry bulk density is in 16B and 16C and shows that the density gradient without flow agent is steeper, the density being higher overall with vibration of 50 to 150 Hz. The addition of superplasticizer leads to a lower density gradient, where even a vibration of 50 Hz is sufficient to produce a homogeneous distribution, while higher frequencies produce increasing density gradients and reduce the dry bulk density.

In 17 the density distribution is shown for test specimens, which are made of starting mixtures with pre-wetted or dry aerated concrete crushed granules. This shows that as a result of the water saturation of the aerated concrete crushed granules prior to addition of the cement to the starting mixture a stiffer consistency is achieved than nominally the same composition in which the volume of water is added to saturate the dry aerated concrete fracture granules with the cement.

The dry bulk density over the height of the test specimens shows higher densities for samples prepared from water-saturated aerated concrete crushed granules in the starting mixture, as such, from starting mixtures prepared with dry aerated concrete crushed granules.

18 shows that overall the degree of compaction was lower in the starting mixture, although the degree of compaction remained substantially unchanged, and resulted in lower compressive strength values after curing for 7 or 28 days of storage. The green strength increased with reduction of the mixing water content. The dry bulk density is higher with reduced mixing water content. Surprisingly, the usual relationship between density and strength is not observed even when reducing the amount of mixing water in the starting mixture, but rather a lower compressive strength is found in the molded block according to the invention despite higher dry bulk density.

The structure of the molded block according to the invention in the core and edge region shows in the microscopic analysis of 19 contiguous particles of the calcium silicate hydrate matrix derived from aerated concrete fracture granules joined by the cement matrix disposed therebetween, the particles of the calcium silicate hydrate matrix being distinguishable from the surrounding cement matrix. Due to the manufacturing process, the distinct particles incorporated into the cementitious matrix are identified as the porous calcium-silicate-hydrate matrix particles of the aerated concrete crushed granules from the starting mixture used.

Claims (13)

A method of producing a cementitious shaped block having a compressive strength of 3 to 20 N / mm ² and a bulk density of 1 to 1.5 kg / dm ^3, comprising the steps of preparing a mixture having an effective water-cement ratio of 0.35 to 0.60 consisting of particles consisting of pre-aerated aerated concrete crushed granules with a particle size of up to 10 mm, 150 to 400 kg / m ^{3 of} hydraulically hardening cement, up to 20% by weight hard coal fly ash, max. 50% by weight of inert aggregates selected from sand, quartz sand and gravel and one volume of water, pressing the mixture at a pressure of 3 to 25 N / mm ² into a mold, the mixture compressing a vibration of 30 to 200 Hz, and allowed to cure the pressed mixture. A method according to claim 1, characterized in that the mixture of particles consisting of aerated concrete crushed granules with a grain size of up to 10 mm, 150 to 400 kg / m ^{3 of} hydraulically hardening cement, up to 20 wt .-% hard coal fly ash and a volume of water , which is sufficient to saturate the suction capacity of the particles of porous calcium silicate hydrate matrix and hydration of the cement consists. A method according to claim 1, characterized in that the mixture consists of aerated concrete crushed granules, water and cement. Method according to one of the preceding claims, characterized in that the volume of water sufficient to saturate the suction capacity of the particles of porous calcium silicate hydrate matrix and hydration of the cement. Method according to one of the preceding claims, characterized in that the particles, which consist of aerated concrete crushed granules, are saturated with water before preparing the mixture. Method according to one of the preceding claims, characterized in that in addition to the cement, a non-hydraulic binder is used. A method according to claim 6, characterized in that the non-hydraulic binder is lime. Method according to one of the preceding claims, characterized in that the mixture comprises a detergent as a liquefying agent. Method according to one of the preceding claims, characterized in that the curing is carried out for 1 to 12 hours in a saturated steam atmosphere at 180 ° C up to 200 ° C. Method according to one of the preceding claims, characterized in that the harden for up to 10 hours is carried out under atmospheric conditions at up to 70 ° C. A shaped brick having a compressive strength of from 3 to 20 N / mm ² and a bulk density of from 1 to 1.5 kg / dm ³ , obtainable by a process comprising the steps of preparing a mixture consisting of particles made of preassessed aerated concrete crushed granules having a grain size of up to 10 mm, 150 to 400 kg / m ^{3 of} hydraulically hardening cement, up to 20% by weight hard coal fly ash, max. 50 wt .-% inert additives selected from sand, quartz sand and gravel, and a volume of water, the pressing of the mixture into a mold and the curing, wherein the pressing was carried out at a pressure of 3 to 25 N / mm ² and the Mixture was subjected to a vibration of 30 to 200 Hz when pressing. A shaped brick according to claim 11, characterized by a green strength of at least 0.2 N / mm ² and a breaking point of at least 5 N / mm ² after 28 days curing at ambient conditions. Use of aerated concrete crushed granules as porous particles of calcium silicate hydrate matrix for the production of shaped bricks in a method according to one of claims 1 to 10.

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